#5000: Eliminate absent arguments in non-strict positions
-+--
Reporter: batterseapower| Owner:
Type: feature request | Status: new
Priority: normal| Component: Compiler
Version: 7.0.2 |Keywords:
Testcase:| Blockedby:
Os: Unknown/Multiple |Blocking:
Architecture: Unknown/Multiple | Failure: Runtime performance bug
-+--
Description changed by batterseapower:
Old description:
One of my programs has this is the output of GHC -O2:
{{{
Rec {
h28_s14N
:: forall t_aMK t_aML.
Main.Nat - t_aMK - t_aML - Main.Nat - Main.Nat
[LclId,
Arity=4,
Unf=Unf{Src=vanilla, TopLvl=True, Arity=4, Value=True,
ConLike=True, Cheap=True, Expandable=True,
Guidance=IF_ARGS [0 0 0 0] 6 2}]
h28_s14N =
\ (@ t_aMK)
(@ t_aML)
(az94z94z941_u439_amh :: Main.Nat)
(awS1_u462_ami :: t_aMK)
(awS1_u466_amj :: t_aML)
(x_u590_amk :: Main.Nat) -
Main.S
(h29_s14O
@ t_aMK
@ t_aML
az94z94z941_u439_amh
awS1_u462_ami
awS1_u466_amj
x_u590_amk)
h29_s14O [Occ=LoopBreaker]
:: forall t_aMK t_aML.
Main.Nat - t_aMK - t_aML - Main.Nat - Main.Nat
[LclId,
Arity=4,
Unf=Unf{Src=vanilla, TopLvl=True, Arity=4, Value=True,
ConLike=True, Cheap=True, Expandable=True,
Guidance=IF_ARGS [0 0 0 5] 9 0}]
h29_s14O =
\ (@ t_aMK)
(@ t_aML)
(az94z94z941_u439_amm :: Main.Nat)
(awS1_u462_amn :: t_aMK)
(awS1_u466_amo :: t_aML)
(x_u590_amp :: Main.Nat) -
case x_u590_amp of _ {
Main.Z - h21'_al8 @ Main.Nat az94z94z941_u439_amm;
Main.S x_u595_amq -
h28_s14N
@ t_aMK
@ t_aML
az94z94z941_u439_amm
awS1_u462_amn
awS1_u466_amo
x_u595_amq
}
end Rec }
}}}
This is ridiculous because the two awS1 arguments are totally dead. This
greatly increases allocations made by the program.
I speculate that this occurs because the recursive call to h29 is guarded
by a use of the S constructor, making it non-strict.
New description:
One of my programs has this is the output of the post-worker/wrapper
simplification:
{{{
Rec {
h28_s14N
:: forall t_aMK t_aML.
Main.Nat - t_aMK - t_aML - Main.Nat - Main.Nat
[LclId,
Arity=4,
Str=DmdType ,
Unf=Unf{Src=vanilla, TopLvl=True, Arity=4, Value=True,
ConLike=True, Cheap=True, Expandable=True,
Guidance=IF_ARGS [0 0 0 0] 6 2}]
h28_s14N =
\ (@ t_aMK)
(@ t_aML)
(az94z94z941_u439_amh :: Main.Nat)
(awS1_u462_ami :: t_aMK)
(awS1_u466_amj :: t_aML)
(x_u590_amk :: Main.Nat) -
Main.S
(h29_s14O
@ t_aMK
@ t_aML
az94z94z941_u439_amh
awS1_u462_ami
awS1_u466_amj
x_u590_amk)
h29_s14O [Occ=LoopBreaker]
:: forall t_aMK t_aML.
Main.Nat - t_aMK - t_aML - Main.Nat - Main.Nat
[LclId,
Arity=4,
Str=DmdType LLLS,
Unf=Unf{Src=vanilla, TopLvl=True, Arity=4, Value=True,
ConLike=True, Cheap=True, Expandable=True,
Guidance=IF_ARGS [0 0 0 3] 7 0}]
h29_s14O =
\ (@ t_aMK)
(@ t_aML)
(az94z94z941_u439_amm :: Main.Nat)
(awS1_u462_amn :: t_aMK)
(awS1_u466_amo :: t_aML)
(x_u590_amp :: Main.Nat) -
case x_u590_amp of _ {
Main.Z - az94z94z941_u439_amm;
Main.S x_u595_amq [Dmd=Just L] -
h28_s14N
@ t_aMK
@ t_aML
az94z94z941_u439_amm
awS1_u462_amn
awS1_u466_amo
x_u595_amq
}
end Rec }
}}}
This is ridiculous because the two awS1 arguments are totally dead. This
greatly increases allocations made by the program.
These absent arguments should be removed by the strictness analyser,
However I speculate that this occurs because the recursive call to h29 is
guarded by a use of the S constructor, making it non-strict.
--
--
Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/5000#comment:1
GHC http://www.haskell.org/ghc/
The Glasgow Haskell Compiler
___
Glasgow-haskell-bugs mailing list
Glasgow-haskell-bugs@haskell.org
http://www.haskell.org/mailman/listinfo/glasgow-haskell-bugs
